1. Field of the Invention
The present invention relates to a pressure transducer and, more particularly, a simplified capacitive pressure transducer including a flexible diaphragm in direct contact with a pressure to be measured. The pressure transducer further includes an insulating substrate defining a plurality of capacitor electrodes sized to accommodate the measurement of pressures within a particular pressure range.
2. Description of the Related Art
High pressure transducers typically generate an output voltage which, ideally, is predictably related to the pressure being measured. Such predictability is often effected by the magnitude of the pressure being measured and by other characteristics of the operating environment. Such predictability could, for example, constitute a linear relationship between the pressure being measured and the output voltage of the transducer. In a pressure transducer of this type, changes in the temperature of the operating environment are known to adversely effect the transducer's performance characteristics by introducing nonlinearities in the output voltage.
U.S. Pat. No. 5,329,819 to Park et al. exemplifies a high pressure transducer of the prior art. The Park et al. transducer includes a thin flexible ceramic diaphragm of low mechanical hysteresis which is mechanically coupled to the pressure being measured through a layer of epoxy and a thick metal diaphragm. Deflection of the thin diaphragm, which serves as an electrode of a variable capacitor, varies a transducer output voltage as described above. It is also noted that the high pressure input fitting employed in the 5,329,819 patent requires a change in diameter, or a plurality of component parts, which increase the cost of the transducer. In addition to the adverse effects of temperature and pressure changes, the performance characteristics of the Park et al. transducer are also influenced by the lack of direct contact between the thin diaphragm and the pressure being measured.
In such prior art transducers, the gap between variable capacitor electrodes must be accurately established and maintained throughout the manufacturing process. To the extent that the number of precision machined parts is reduced by employing welding as a step in the assembly process, the cost of manufacturing pressure transducers can be reduced. However, caution must be exercised not to apply excess heat to materials near the gap of the variable capacitor. Otherwise, the gap dimensions might be intolerably and irreversibly changed by the thermal expansion of the materials surrounding the gap. Thus, the prior art lacks a capacitive high pressure transducer which is easily and affordably assembled while maintaining accurate gap tolerances for the duration of the assembly procedure.
Accordingly, an object of the present invention is to provide a capacitive high pressure transducer wherein a gap between variable capacitor electrodes of the transducer is accurately established and maintained during assembly of the transducer.
Another object is to provide a pressure transducer which utilizes selected materials to anticipate and compensate for thermal expansions of these materials during assembly of the transducer.
Another object is to provide a capacitive pressure transducer with superior performance characteristics over varying pressures and temperatures.
Another object is to provide a capacitive pressure transducer with a flexible variable capacitor electrode which is in direct contact with the pressure being measured.
Another object is to provide a simplified capacitive high pressure transducer which is more simply and economically assembled from fewer components.